A power transmission belt, such as a V-ribbed belt, is generally formed by laminating an adhesion rubber layer having a cord embedded therein and a compression rubber layer provided on the surface of the adhesion rubber layer located near the inner periphery of the belt. In addition to these materials, a backing rubber layer is provided on the surface of the adhesion rubber layer located near the outer periphery of the belt, thereby increasing the power transmission ability during power transmission on the back face of the belt.
PATENT DOCUMENT 1 describes that a monofilament with a flat cross section is embedded in a backing rubber layer of a V-ribbed belt, and further describes that such a structure can prevent rib rubber from being longitudinally split along grooves between V-ribs.
PATENT DOCUMENT 2 describes a structure in which a backing rubber layer of a V-ribbed belt is made of a rubber composition containing an ethylene-α-olefin elastomer with an ethylene content of 40-60% and a Mooney viscosity of 40-60 as raw rubber, and further in which the total amount of addition of reinforcing short fibers to the backing rubber layer is 0-30 parts by weight (pbw) per 100 pbw of rubber. PATENT DOCUMENT 2 further describes that such a structure provides excellent bending fatigue resistance, heat resistance, cold resistance, wear resistance, and adhesion resistance.